Implement node monitoring in the kernel disk device manager.

* Added {Create|Delete}Device() analogous to {Create|Delete}FileDevice
* Added a small DeviceWatcher class that reacts to entry creation/removal
* Implemented a way to start/stop node monitoring
* Start watching for devices after the boot volume has been mounted and the
  the second initial scan was run

The disk device manager now creates and scans a device when a "raw" node is
published and deletes the device on removal. This makes hot-plugging of disk
devices (for example memory sticks using usb_disk) work. Their partitions will
be scanned and published so they can be mounted. Somehow the removal of the
partitions does not yet work however, any insights are welcome.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@24777 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/disk_device_manager/KDiskDeviceManager.h

@@ -65,6 +65,9 @@ public:
 
 	status_t ScanPartition(KPartition* partition);
 
+	partition_id CreateDevice(const char *path, bool *newlyCreated = NULL);
+	status_t DeleteDevice(const char *path);
+
 	partition_id CreateFileDevice(const char* filePath,
 		bool* newlyCreated = NULL);
 	status_t DeleteFileDevice(const char *filePath);
@@ -90,13 +93,9 @@ public:
 	KDiskSystem *LoadDiskSystem(disk_system_id id);
 	KDiskSystem *LoadNextDiskSystem(int32 *cookie);
 
-	// Watching
-
-	// TODO: Watching service for the kernel. The userland watching is handled
-	// by the registrar.
-
 	status_t InitialDeviceScan();
 	status_t RescanDiskSystems();
+	status_t StartMonitoring();
 
 private:
 	static status_t _CheckMediaStatusDaemon(void* self);
@@ -117,10 +116,13 @@ private:
 	status_t _ScanPartition(KPartition *partition);
 		// used by the other _ScanPartition() version only
 
+	status_t _AddRemoveMonitoring(const char *path, bool add);
+
 	struct DeviceMap;
 	struct DiskSystemMap;
 	struct PartitionMap;
 	struct PartitionSet;
+	class DeviceWatcher;
 
 	BLocker						fLock;
 	DeviceMap					*fDevices;
@@ -129,6 +131,7 @@ private:
 	PartitionSet				*fObsoletePartitions;
 	thread_id					fMediaChecker;
 	volatile bool				fTerminating;
+	DeviceWatcher				*fDeviceWatcher;
 
 	static KDiskDeviceManager	*sDefaultManager;
 };